Method and apparatus for reusing DHCP addresses in home addresses of mobile IP clients

ABSTRACT

Methods and apparatuses for conserving addresses. The invention allows a mobile node to manage its own address, shifting responsibility away from the home agent. The home agent is able to detect when a mobile node has already been assigned an address for use of resources on the network. When the home agent recognizes that the mobile address has already been assigned an address, it allows the mobile node to use its already-assigned address in connection with mobile IP services. Additionally, the mobile node can be notified that it is now responsible for renewing the address.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/362,251, filed Mar. 5, 2002, incorporated herein byreference in its entirety and for all purposes. This application isrelated to Ser. No. 10/150,377, filed May 17, 2002, and Ser. No.10/187,084, filed Jun. 28, 2002, both of which are incorporated hereinby reference in their entireties and for all purposes, and both of whichalso claim benefit of U.S. Provisional Application No. 60/362,251, filedMar. 5, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to mobile computing andmore specifically to management of addresses for mobile nodes.

[0004] 2. Description of the Related Art

[0005] Mobile IP is a protocol that allows laptop computers and othermobile computer units (“mobile nodes”) to roam between varioussub-networks while maintaining Internet and/or WAN connectivity. WithoutMobile IP or similar protocols a mobile node would be unable to stayconnected while roaming from one location serviced by one sub-network toanother location being serviced by a different sub-network. This isbecause each IP address has a field that specifies the particularsub-network on which the node resides. If a user desires to take acomputer that is normally attached to one node and roam so that itpasses through different sub-networks, the roaming computer cannot useits home base IP address. As a result, a businessperson traveling acrossthe country cannot travel with his or her computer across geographicallydisparate network segments or wireless nodes while maintaining Internetconnectivity. This is not acceptable in the age of portablecomputational devices.

[0006] To address this problem, the Mobile IP protocol has beendeveloped and implemented. An implementation of Mobile IP is describedin RFC 3220, “IP Mobility Support for IPv4” of the Network WorkingGroup, C. Perkins, Ed., January 2002. Mobile IP is also described in thetext “Mobile IP, The Internet Unplugged” by J. Solomon, Prentice Hall,1998. Both of these references are incorporated herein by reference intheir entireties and for all purposes.

[0007] The Mobile IP process and environment are illustrated in FIG. 1.A Mobile IP environment 100 includes the Internet (or a WAN) 105 overwhich a mobile node 110 can communicate via mediation by a home agent115 or a foreign agent 120. Typically, the home agent 115 and foreignagent 120 are routers or other network connection devices performingappropriate Mobile IP functions as implemented by software, hardware,and/or firmware. Note the overall network topology is arbitrary, andelements such as the home agent 115 need not directly connect to theInternet 105. For example, the home agent 115 may be connected throughanother router R2 125. Router R2 125 may, in turn, connect one or moreother routers R3 130 with the Internet 105.

[0008] When mobile node 110 is plugged into its home network segment 135it connects with the Internet 105 through its designated home agent 115.When the mobile node 110 roams, it can be connected to a remote networksegment 140 and communicate through the available foreign agent 120.Other nodes, such as a PC 145, on remote network segment 140 alsocommunicate with the Internet 105 through foreign agent 120. Presumably,there are many foreign agents available at geographically disparatelocations to allow wide spread Internet connection via the Mobile IPprotocol.

[0009] Mobile node 110 may identify foreign agent 120 through variousagent solicitations and agent advertisements that form part of theMobile IP protocol. When mobile node 110 engages with remote networksegment 140, it composes a registration request for the home agent 115to bind the mobile node's 110 current location with its home location.Foreign agent 120 then relays the registration request 150 to home agent115. During the registration process, the home agent 115 and the mobilenode 110 may then negotiate the conditions of the mobile node's 110attachment to foreign agent 120. For example, the mobile node 110 mayrequest a registration lifetime of 5 hours, but the home agent 115 maygrant only a 3 hour period. When the negotiation is successfullycompleted, home agent 115 updates an internal “mobility binding table”which links the mobile node's 110 current location via its care-ofaddress (e.g., a co-located care-of address or the foreign agent's IPaddress) to the identity (e.g., home address) of the mobile node 110.Further, if the mobile node 110 registered via foreign agent 120, theforeign agent 120 updates an internal “visitor table” which specifiesthe mobile node address, home agent address, etc. The home agent's 115association between a mobile node's home base IP address, its currentcare-of address, and the remaining lifetime of that association isreferred to as a binding.

[0010] If mobile node 110 wanted to send a message to a correspondentnode 155 from its new location, the mobile node 110 would forward apacketized output message 160 through the foreign agent 120 over theInternet 105 to the correspondent node 155 according to standardInternet protocols. However, if the correspondent node 155 wanted tosend a message 165 to the mobile node 110—whether in reply to a messagefrom the mobile node 110 or for any other reason—the correspondent node155 addresses that message to the IP address of the mobile node 110 asif the mobile node 110 were on the home network segment 135. The packetsof the message from the correspondent node 155 are forwarded over theInternet 105 to the router R2 125 and ultimately to the home agent 115.

[0011] From the home agent's 115 mobility binding table, the home agent115 recognizes that the mobile node 110 is no longer attached to thehome network segment 135. The home agent 115 then encapsulates thepackets from correspondent node 155 (which are addressed to the mobilenode 110 on the home network segment 135) according to the Mobile IPprotocol, and forwards these encapsulated packets 170 to the appropriatecare-of address for mobile node 110. If the care-of address is the IPaddress of the foreign agent 120 the foreign agent 120 strips theencapsulation and forwards the message to the mobile node 110 on theremote network segment 140. The packet forwarding mechanism implementedby the home agent 115 to the foreign agent 120 is often referred to as“tunneling.”

[0012] As set forth in RFC 3220, the Mobile IP specification, the mobilenode 110 can be statically provisioned with its home address or requesthome address assignment. Home address assignment is typically requestedby setting the home address field of the registration request to 0.0.0.0and using a mobile node network address identifier (NAI) extension toidentify itself. NAI is described in RFC 2794 of the Network WorkingGroup, P. Calhoun and C. Perkins, March 2000, incorporated herein byreference in its entireties and for all purposes. After receiving andauthenticating such a registration request, the home agent is expectedto assign a home address to the mobile node in the registration reply.

[0013] One proposal for home address assignment by the home agent isdescribed in the IETF working group draft, “Mobile IP Agents as DHCPProxies,” S. Glass, draft-glass-mobileip-agent-dhcp-proxy-01.txt, Mar.2, 2000, incorporated herein by reference in its entirety and for allpurposes. In that draft, the home agent behaves as a DHCP proxy agent,acting on behalf of the mobile node. However, having the home agentinvolved in address management (assignment, renewal, release etc) is anoverhead, especially in enterprise networks.

SUMMARY OF THE INVENTION

[0014] The present invention provides methods and apparatuses forconserving addresses. In one embodiment a mobile node requests anassignment of a first address so that the first address could be used tofacilitate the mobile node's use of network resources. For instance, thefirst address may be an address allocated by a DCHP server. The mobilenode also requests an assignment of a second address so that the secondaddress could be used to facilitate the mobile node's ability tomaintain connectivity while roaming. For instance, the request forassignment of the second address may be a Mobile IP registration requestrequesting a home address as the second address. The mobile node thenuses a single address as both the first address and the second address

[0015] In another embodiment a home agent receives a request forassignment of a first address. The home agent then routes the requestfor assignment to a server that can satisfy the request. The home agentalso receives a request for assignment of a second address. The homeagent then recognizes that the request for assignment of the firstaddress and the request for assignment of the second address came from asingle device. The home agent would then alert the single device to usea single address to satisfy both requests.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram of a Mobile IP environment;

[0017]FIG. 2 is a block diagram illustrating an exemplary environment inwhich the present invention may be implemented;

[0018]FIG. 3 is a control flow diagram illustrating a method of allowinga mobile node to use the same IP address it was initially assigned withDHCP for Mobile IP purposes when the mobile node boots up on the homeagent's network segment;

[0019]FIG. 4 is a diagram illustrating an exemplary network device inwhich various embodiments of the invention may be implemented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In the following description, numerous specific details are setforth to provide a thorough understanding of the present invention. Itwill be obvious, however, to one skilled in the art that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps have not beendescribed in detail in order to avoid unnecessarily obscuring thepresent invention.

[0021] When a mobile node first connects to a network, it is assigned anIP address so that it can access network resources. The presentinvention allows a mobile node to use the same IP address initiallyassigned to it for mobile IP purposes. As a consequence, the mobile nodecan manage its own address, removing the burden of management from thehome agent. Moreover, the home agent need not assign an additionaladdress to the mobile node, thereby conserving IP addresses.

[0022]FIG. 2 is a block diagram illustrating an exemplary environment inwhich the present invention may be implemented. An internal network 205,having a home agent 210, a foreign agent 215 and a Dynamic HostConfiguration Protocol (DHCP) server 220 is connected to the Internet225, which is connected to an external network 230, having an externalforeign agent 235 and an external DHCP server 240.

[0023] DHCP is based on the Bootstrap Protocol (BOOTP), an Internetprotocol that enables a diskless workstation to discover its own IPaddress. DHCP is described in RFC 2131 of the Network Working Group, R.Droms, March 1997, and BOOTP is described in RFC 951 of the NetworkWorking Group, B. Croft, September 1985, both references incorporatedherein by reference in their entirety and for all purposes. RFC 2131defines a DHCP server as a host that provides initialization parametersthrough DHCP. Essentially, a DHCP server allows IP addresses to bedynamically assigned to devices on a network. Dynamic addressingsimplifies network administration because the software keeps track of IPaddresses rather than requiring an administrator to statically provisionthe IP address for every device on the network. Current MicrosoftWindows® operating systems have integrated DHCP client support.

[0024] Referring back to FIG. 2, once a mobile node 245 with MicrosoftWindows® boots up it must obtain an IP address from a DHCP server. Ifthe mobile node 245 boots up in the internal network 205 (i.e., oneither the home agent's 210 or the foreign agent's 215 network segment),the internal DHCP server 220 will be responsible for assigning aninitial IP address. If the mobile node 245 boots up in the externalnetwork 230 (i.e., on the external foreign agent's 235 network segment),the external DHCP server 240 will assign the mobile node 245 its initialIP address. Only after it obtains an address can the mobile node 245begin Mobile IP registration.

[0025]FIG. 3 is a control flow diagram illustrating a method of allowinga mobile node to use the same IP address it was initially assigned withDHCP for Mobile IP purposes when the mobile node 230 boots up on thehome agent's 210 network segment. Steps performed by the mobile node230, the home agent 210 and DHCP server 220 are represented bycorresponding vertical lines 305, 310, and 315.

[0026] At 320 the mobile node 230 attempts to locate DHCP services bysending a broadcast (DHCPDISCOVER) to the home agent 210. Although themobile node 230 cannot include an IP address in the DHCP discover packet(an IP address has not yet been assigned) it can include its link-layeraddress. A link-layer address is defined in RFC 3220 as, “The addressused to identify an endpoint of some communication over a physical link.Typically, the Link-Layer address is an interface's Media Access Control(MAC) address.”

[0027] At 325 the home agent 210, in its capacity as a DHCP/BOOTP relayagent, processes the DHCPDISCOVER, which includes substituting its ownIP address into the DHCPDISCOVER message and noting the interface fromwhich the DHCPDISCOVER originated. At 330 the home agent 210 relays theDHCPDISCOVER message to the DHCP server 220.

[0028] At 335 the DHCP server 220 performs its standard authenticationsand negotiations with the mobile node 230, via the home agent 210, asrequired by RFC 2131. At 340 the DHCP server 220 sends itsacknowledgement (DHCPACK) to the home agent 210. The DHCPACK containsall the necessary configuration parameters for the mobile node 245including the IP address and link-layer address mapping.

[0029] At 345 the home agent 210 recognizes the DHCPACK message andoptionally maintains a mapping between the DHCP allocated IP address andthe link-layer address. For instance, in one embodiment, the home agent210 caches the IP address, link-layer address mapping and interfaceinformation. Several options are available for maintenance of the cachedinformation. In one embodiment, the mapping is kept in a table until thetable is filled up, and then the oldest entries are replaced by newerentries. Therefore, if the table could, for example, hold 1000 entries,the 1001st entry would replace the first entry. Additionally, when themobile node 245 renews its lease on its IP address, the more recentDCHPACK could replace the older mapping.

[0030] At 350 the home agent 210 forwards the DHCPACK message to themobile node 245. At 355 the mobile node processes the DHCPACK andobtains the IP address assigned by the DHCP server 220 from the DHCPACK.In addition, the mobile node may also obtain the lease time associatedwith the IP address from the DHCPACK so the mobile node can manage theIP address and associated lease time.

[0031] As per RFC 3220, when the mobile node sends a registrationrequest, the mobile node can indicate that it is requesting a homeaddress by setting the home address field of the registration request tozero and by identifying itself in an NAI extension.

[0032] At 360 the mobile node 245 sends a registration request thatrequests a home agent and home address assignment. In one embodiment, ageneric home agent domain name (e.g., ha.cisco.com) is additionallyprovided in a generalized network access identifier extension (GNAIE).The GNAIE is fully described in the IETF working group draft“Generalized NAI (GNAI) Extension for Mobile IPv4,” Khalil, M.,Qaddoura, E, Akhtar, H., and Calhoun, P.,draft-ietf-mobileip-gnaie-05.txt, October 2001, incorporated herein byreference in its entirety and for all purposes.

[0033] At 365 the home agent 210 recognizes the message as a Mobile IPregistration request coming from a mobile node that previously receiveda DHCP address assignment. In embodiments where the cached table isused, the source address in the registration request and/or theinterface that the registration request arrived from can be checkedagainst the cached table of entries to determine if the mobile node 245was previously assigned an IP address. Alternatively, the home agent 210can recognize that it is in the same domain (e.g., cisco.com) as thedomain specified in the NAI. Other extensions could also be appending tothe registration request that signal the mobile node's ability to manageits own address. In other embodiments, the home agent 210 wouldrecognize the source IP address as being on the same network as the homeagent 210. In yet other embodiments, the home agent 210 would recognizethat the registration request originated from one of its own interfaces.

[0034] Once the home agent 210 determines that the mobile node 245 wasassigned a DHCP address, it would then process the registration requestnormally. At 370 the home agent 210 would send a registration reply tothe mobile node 245, setting the home address field of the registrationreply equal to the DHCP address. In addition, the NAI extension andGNAIE extension may also be appended to the registration reply.

[0035] At 375 the mobile node 245 recognizes that it is in charge of itsown address management using DHCP. One mechanism that can be used toalert the mobile node 245 that it is in charge of managing its ownaddress and associated lease time is by the home agent 210 appending aspecial extension to the registration reply. Another mechanism could befor the mobile node to compare its DHCP address with the home agentaddress in the registration reply.

[0036] The mobile node 245, therefore, does not discard the originalDHCP information. Additionally, when it is time for the mobile node 245to renew its lease on the DHCP address, it will send the appropriaterenewal message (DHCPREQUEST). Since the DHCPREQUEST is a standard IPpacket it will be routed as any other IP packet. Therefore, if themobile node 245 roamed to the foreign agent 215, the foreign agent wouldreverse tunnel the message to the home agent 210, and the home agent 210will route the DHCPREQUEST to the DHCP server 220 normally. Similarly,the home agent 210 would tunnel the DHCP server's 220 responses asnormal IP packets back to the foreign agent 215, for routing to themobile node 245. If the home agent 210 is maintaining a table, it couldupdate its entries based on any DHCPACK received from renewal requests.

[0037] As one skilled in the art will appreciate, the mobility bindingsalso need to be periodically refreshed according to the Mobile IPprotocol. Using any of the techniques described in connection with 365,the home agent 210 could recognize that the mobile node 245 is managingits own IP address. The home agent 210 would process the requestnormally, except it would not attempt to manage the mobile node's 245 IPaddress allocated by the DHCP server.

[0038] Additionally, it should be appreciated that if the mobile node245 does not roam from its home agent 210 the Mobile IP protocol treatsthe mobile node 245 as a stationary node, without making use of anyother Mobile IP functionality. However, the mobile node 245 cachesinformation about its home agent 210 until it is powered off, allowingit to roam at a later time. Therefore, if the mobile node 245 receivesan agent advertisement from the home agent 210, it will deregister inaccordance with Mobile IP protocol. Since routing will allow traffic tobe sent to and from the mobile node 245 while it is attached to its homeagent 210, the invention does not require any further modifications toMobile IP processing when the mobile node 245 acts as a stationary node.

[0039] If the mobile node 245 boots up in an external foreign agent's235 service provider network (See FIG. 2), it registers with the homeagent 210, and home address assignment can be performed as per thedescription in the previously mentioned “Mobile IP Agents as DHCPProxies.” This implementation can be optimized so that home agents arecentralized when the mobile node 245 is registering from the externalnetwork 230. Thus, even if the mobile node 245 roams back to theinternal network 205, the home agent 210 will continue to act as a proxyfor the mobile node 245 and the mobile node 245 will not deregisteruntil it power offs.

[0040] Generally, the techniques of the present invention may beimplemented on software and/or hardware. For example, they can beimplemented in an operating system kernel, in a separate user process,in a library package bound into network applications, on a speciallyconstructed machine, or on a network interface card. In a specificembodiment of this invention, the technique of the present invention isimplemented in software such as an operating system or in an applicationrunning on an operating system.

[0041] A software or software/hardware hybrid implementation of thetechniques of this invention may be implemented on a general-purposeprogrammable machine selectively activated or reconfigured by a computerprogram stored in memory. Such a programmable machine may be a networkdevice designed to handle network traffic, such as, for example, arouter or a switch. Such network devices may have multiple networkinterfaces including frame relay and ISDN interfaces, for example.Specific examples of such network devices include routers and switches.For example, home agents, and foreign agents of this invention may beimplemented in specially configured routers, switches or servers, suchas specially configured router models 2600, 3200, 3600, 4500, 7200, and7500 available from Cisco Systems, Inc. of San Jose, Calif. A generalarchitecture for some of these machines will appear from the descriptiongiven below. In an alternative embodiment, the techniques of thisinvention may be implemented on a general-purpose network host machinesuch as a personal computer or workstation. Further, the invention maybe at least partially implemented on a card (e.g., an interface card)for a network device or a general-purpose computing device.

[0042] Referring now to FIG. 4, a network device 400 suitable forimplementing the techniques of the present invention includes a mastercentral processing unit (CPU) 405, interfaces 410, memory 415 and a bus420. When acting under the control of appropriate software or firmware,the CPU 405 may be responsible for implementing specific functionsassociated with the functions of a desired network device. For example,when configured as an intermediate router, the CPU 405 may beresponsible for analyzing packets, encapsulating packets, and forwardingpackets for transmission to a set-top box. The CPU 405 preferablyaccomplishes all these functions under the control of software includingan operating system (e.g. Windows NT), and any appropriate applicationssoftware.

[0043] CPU 405 may include one or more processors such as those from theMotorola family of microprocessors or the MIPS family ofmicroprocessors. In an alternative embodiment, the processor isspecially designed hardware for controlling the operations of networkdevice 400.

[0044] The interfaces 410 are typically provided as interface cards(sometimes referred to as “line cards”). Generally, they control thesending and receiving of data packets over the network and sometimessupport other peripherals used with the network device 400. Among theinterfaces that may be provided are Ethernet interfaces, frame relayinterfaces, cable interfaces, DSL interfaces, token ring interfaces, andthe like. In addition, various very high-speed interfaces may beprovided such as fast Ethernet interfaces, Gigabit Ethernet interfaces,ATM interfaces, HSSI interfaces, POS interfaces, FDDI interfaces, ASIinterfaces, DHEI interfaces and the like. Generally, these interfacesmay include ports appropriate for communication with the appropriatemedia. In some cases, they may also include an independent processorand, in some instances, volatile RAM. The independent processors maycontrol such communications intensive tasks as packet switching, mediacontrol and management. By providing separate processors for thecommunications intensive tasks, these interfaces allow the CPU 405 toefficiently perform routing computations, network diagnostics, securityfunctions, etc.

[0045] Although the system shown in FIG. 4 illustrates one specificnetwork device of the present invention, it is by no means the onlynetwork device architecture on which the present invention can beimplemented. For example, an architecture having a single processor thathandles communications as well as routing computations, etc. is oftenused. Further, other types of interfaces and media could also be usedwith the network device.

[0046] Regardless of network device's configuration, it may employ oneor more memories or memory modules (such as, for example, the memory415) configured to store data, program instructions for thegeneral-purpose network operations and/or other information relating tothe functionality of the techniques described herein. The programinstructions may control the operation of an operating system and/or oneor more applications, for example.

[0047] Because such information and program instructions may be employedto implement the systems/methods described herein, the present inventionrelates to machine readable media that include program instructions,state information, etc. for performing various operations describedherein. Examples of machine-readable media include, but are not limitedto, magnetic media such as hard disks, floppy disks, and magnetic tape;optical media such as CD-ROM disks; magneto-optical media such asfloptical disks; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory devices(ROM) and random access memory (RAM). The invention may also be embodiedin a carrier wave traveling over an appropriate medium such as airwaves,optical lines, electric lines, etc. Examples of program instructionsinclude both machine code, such as produced by a compiler, and filescontaining higher level code that may be executed by the computer usingan interpreter.

[0048] Although illustrative embodiments and applications of thisinvention are shown and described herein, many variations andmodifications are possible which remain within the concept, scope, andspirit of the invention, and these variations would become clear tothose of ordinary skill in the art after perusal of this application.For instance, the present invention is described as being configured tocomply with Mobile IP standards in force as of the time this documentwas written. However, it should be understood that the invention is notlimited to such implementations. Accordingly, the present embodimentsare to be considered as illustrative and not restrictive, and theinvention is not to be limited to the details given herein, but may bemodified within the scope and equivalents of the appended claims.

What is claimed is:
 1. In a home agent, a method of processing aregistration request received from a Mobile Node, comprising: receivinga request for assignment of a DHCP address from a DHCP server, therequest being received from a Mobile Node; routing the request forassignment of the DHCP address to the DHCP server; receiving aregistration request from the mobile node, the registration requestrequesting assignment of a home address to the mobile node; and sendinga registration reply to the mobile node, the registration replyindicating that the mobile node is to use the DHCP address as the homeaddress.
 2. The method as recited in claim 1, further comprising;receiving the DHCP address from the DHCP server; and providing the DHCPaddress received from the DHCP server to the mobile node.
 3. The methodas recited in claim 2, further comprising: receiving a lease timeassociated with the DHCP address from the DHCP server; and providing thelease time associated with the DHCP server to the mobile node.
 4. Themethod as recited in claim 3, wherein the registration reply indicatesthat the mobile node is to manage the DHCP address and the lease timeassociated with the DHCP address.
 5. The method as recited in claim 1,further comprising: processing the registration request such that abinding is maintained between the mobile node and the DHCP address. 6.The method as recited in claim 1, wherein the registration replyindicates that the mobile node is to manage the DHCP address andassociated lease time.
 7. The method as recited in claim 1, furthercomprising: determining whether the mobile node and the home agent arein the same domain; wherein sending the registration reply indicatingthat the mobile node is to use the DHCP address as the home address isperformed when it has been determined that the mobile node and the homeagent are in the same domain.
 8. The method as recited in claim 1,further comprising: obtaining the DHCP address from the registrationrequest; and setting the home address field of the registration reply tothe DHCP address.
 9. The method as recited in claim 1, furthercomprising: maintaining a mapping between the DHCP address and alink-layer address associated with the mobile node.
 10. A method ofconserving addresses comprising: receiving a request for assignment of afirst address; routing the request for assignment to a server that cansatisfy the request; receiving a request for assignment of a secondaddress; recognizing that the request for assignment of the firstaddress and the request for assignment of the second address came from asingle device; and alerting the single device to use a single address tosatisfy both requests.
 11. The method of claim 10, wherein the firstaddress is to be used by the single device to facilitate the singledevice's use of network resources.
 12. The method of claim 10, whereinthe second address is to be used by the single device to facilitate thesingle device's ability to maintain connectivity while roaming.
 13. Themethod of claim 10, wherein recognizing is accomplished by analyzing anextension accompanying the request for assignment of the second address.14. The method of claim 13, wherein the extension is a GNAIE.
 15. Themethod of claim 10, wherein recognizing is accomplished by analyzing thesource of the request for assignment of the second address.
 16. Themethod of claim 10, further comprising storing information relating tothe request for assignment of the first address.
 17. The method of claim16, wherein recognizing is accomplished by comparing informationrelating to the request for assignment of the second address with thestored information.
 18. The method of claim 10, further comprisingsending a registration reply to the single device in response to therequest for assignment of the second address.
 19. The method of claim18, wherein alerting is accomplished by appending an extension to theregistration reply.
 20. The method of claim 18, wherein alerting isaccomplished by assigning the single address to the second address inthe registration reply and allowing the single device to compare theassigned first address with the assigned second address.
 21. The methodof claim 18, wherein alerting is accomplished by setting the homeaddress field of the registration reply to the single address, whereinthe second address is the home address.
 22. The method as recited inclaim 20, wherein the single address is the first address.
 23. Themethod as recited in claim 22, wherein the first address is an addressassigned by a DHCP server.
 24. The method of claim 10, wherein thesingle device initiates its own renewal procedures.
 25. A mobile IPnetwork device comprising: a processor; memory, operably connected withthe processor; and a network interface, operably connected with theprocessor; wherein the processor is operable to perform instructionsincluding receiving a request for assignment of a first address; routingthe request for assignment to a server that can satisfy the request;receiving a request for assignment of a second address; recognizing thatthe request for assignment of the first address and the request forassignment of the second address came from a single device; and alertingthe single device to use a single address to satisfy both requests. 26.The mobile IP network device of claim 25, wherein the first address isto be used by the single device to facilitate the single device's use ofnetwork resources.
 27. The mobile IP network device of claim 25, whereinthe second address is to be used by the single device to facilitate thesingle device's ability to maintain connectivity while roaming.
 28. Themobile IP network device of claim 25, wherein recognizing isaccomplished by analyzing an extension accompanying the request forassignment of the second address.
 29. The mobile IP network device ofclaim 28, wherein the extension is a GNAIE.
 30. The mobile IP networkdevice of claim 25, wherein recognizing is accomplished by analyzing thesource of the request for assignment of the second address.
 31. Themobile IP network device of claim 25, wherein the processor is operableto further perform instructions that include storing informationrelating to the request for assignment of the first address.
 32. Themobile IP network device of claim 31, wherein recognizing isaccomplished by comparing information relating to the request forassignment of the second address with the stored information.
 32. Themobile IP network device of claim 25, wherein the processor is operableto further perform instructions that include sending a registrationreply to the single device in response to the request for assignment ofthe second address.
 33. The mobile IP network device of claim 32,wherein alerting is accomplished by appending an extension to theregistration reply.
 34. The mobile IP network device of claim 32,wherein alerting is accomplished by assigning the single address to thesecond address in the registration reply and allowing the single deviceto compare the assigned first address with the assigned second address.35. The mobile IP network device of claim 32, wherein alerting isaccomplished by setting the home address field of the registration replyto the single address, wherein the second address is the home address.36. The method as recited in claim 34, wherein the single address is thefirst address.
 37. The method as recited in claim 36, wherein the firstaddress is an address assigned by a DHCP server.
 38. The mobile IPnetwork device of claim 25, wherein the single device initiates its ownrenewal procedures.
 39. A computer program product comprising: acomputer usable medium having computer readable code embodied therein,the computer readable code including computer code for requestingassignment of a first address, the first address to be used tofacilitate a mobile node's use of network resources; requestingassignment of a second address, the second address to be used tofacilitate the mobile node's ability to maintain connectivity whileroaming; and using a single address as both the first address and thesecond address.
 40. The computer program product of claim 39, whereinthe first address is to be used by the single device to facilitate thesingle device's use of network resources.
 41. The computer programproduct of claim 39, wherein the second address is to be used by thesingle device to facilitate the single device's ability to maintainconnectivity while roaming.
 42. The computer program product of claim39, wherein recognizing is accomplished by analyzing an extensionaccompanying the request for assignment of the second address.
 43. Thecomputer program product of claim 42, wherein the extension is a GNAIE.44. The computer program product of claim 39, wherein recognizing isaccomplished by analyzing the source of the request for assignment ofthe second address.
 45. The computer program product of claim 39,wherein the computer readable code includes computer code for storinginformation relating to the request for assignment of the first address.46. The computer program product of claim 45, wherein recognizing isaccomplished by comparing information relating to the request forassignment of the second address with the stored information.
 47. Thecomputer program product of claim 39, wherein the computer readable codeincludes computer code for sending a registration reply to the singledevice in response to the request for assignment of the second address.48. The computer program product of claim 47, wherein alerting isaccomplished by appending an extension to the registration reply. 49.The computer program product of claim 47, wherein alerting isaccomplished by assigning the single address to the second address inthe registration reply and allowing the single device to compare theassigned first address with the assigned second address.
 50. Thecomputer program product of claim 47, wherein alerting is accomplishedby setting the home address field of the registration reply to thesingle address, wherein the second address is the home address.
 51. Themethod as recited in claim 49, wherein the single address is the firstaddress.
 52. The method as recited in claim 51, wherein the firstaddress is an address assigned by a DHCP server.
 53. The computerprogram product of claim 39, wherein the single device initiates its ownrenewal procedures.
 54. A home agent comprising: means for receiving arequest for assignment of a first address; means for routing the requestfor assignment to a server that can satisfy the request; means forreceiving a request for assignment of a second address; means forrecognizing that the request for assignment of the first address and therequest for assignment of the second address came from a single device;and means for alerting the single device to use a single address tosatisfy both requests.
 55. A method of conserving addresses comprising:requesting assignment of a first address, the first address to be usedto facilitate a mobile node's use of network resources; requestingassignment of a second address, the second address to be used tofacilitate the mobile node's ability to maintain connectivity whileroaming; and using a single address as both the first address and thesecond address.
 56. A mobile node comprising: means for requestingassignment of a first address, the first address to be used tofacilitate a mobile node's use of network resources; and means forrequesting assignment of a second address, the second address to be usedto facilitate the mobile node's ability to maintain connectivity whileroaming; wherein a single address is used as both the first address andthe second address.
 57. A mobile IP network device comprising: aprocessor; memory, operably connected with the processor; and a networkinterface, operably connected with the processor; wherein the processoris operable to perform instructions including requesting assignment of afirst address, the first address to be used to facilitate a mobilenode's use of network resources; requesting assignment of a secondaddress, the second address to be used to facilitate the mobile node'sability to maintain connectivity while roaming; and using a singleaddress as both the first address and the second address.
 58. A computerprogram product comprising: a computer usable medium having computerreadable code embodied therein, the computer readable code includingcomputer code for requesting assignment of a first address, the firstaddress to be used to facilitate a mobile node's use of networkresources; requesting assignment of a second address, the second addressto be used to facilitate the mobile node's ability to maintainconnectivity while roaming; and using a single address as both the firstaddress and the second address.
 59. The computer program product ofclaim 58, wherein requesting assignment of the first address isperformed in the context of a DHCPDISCOVER message.
 60. The computerprogram product of claim 59, wherein the single address is received in aDHCPACK message.
 61. The computer program product of claim 58, whereinrequesting assignment of the second address is performed in the contextof a Mobile IP registration request.
 62. The computer program product ofclaim 58, wherein the computer readable code includes computer code for:receiving a registration response in response to requesting assignmentof the second address; and recognizing that the single address must bemanaged by the mobile node.
 63. The computer program product of claim62, wherein recognizing is accomplished by interpreting an extension tothe registration reply.
 63. The computer program product of claim 62,wherein recognizing is accomplished by determining that the firstaddress is the same as the second address.
 64. The computer programproduct of claim 58, wherein the computer readable code includescomputer code for managing the single address.
 65. The computer programproduct of claim 58, wherein the computer readable code includescomputer code for requesting that the mobility bindings be refreshed.66. The computer program product of claim 58, wherein the device is usedin a Mobile IP environment.